He was fined £550, ordered to pay his victim £100 compensation and told to pay £55 victims’ surcharge by Blackpool magistrates.

Alison Quanbrough, prosecuting, said a 55-year-old man and his wife had been on a night out and were waiting for a taxi outside the C Cabs office on November 9 about midnight. Robertson walked up and punched the victim in the face.

The victim’s spectacles were knocked off and he could not see. Robertson hit him twice more in the face and the victim could hear his wife screaming. The victim, who suffered a lump under the eye and abrasions, said the defendant was a stranger and it was an unprovoked assault.

Robertson told police he had drunk five vodka and cokes with friends. He then went into another pub and after that he had no memory of what happened.

Peter Manning, defending, said the reason behind the attack was likely to remain a mystery, but the assault was out of character for Robertson.

Robertson, a former doorman who had been in the Army for eight years serving in Kosovo, Iraq and Sierra Leone, thought it was possible his drink had been spiked.